Wall of questions near the Grenfell Tower in Latimer Road, west London.
Photograph: Graeme Robertson for the Guardian

How many people actually died?

Police said this week they believed the number of people who died in the blaze would remain at about 80, adding that claims that hundreds were still missing were incorrect. However, there remains scepticism about this number among survivors and relatives of the dead, many of whom say the final death toll could be higher.

The suspicion of police numbers was fuelled in the days immediately after the fire, when the official number of confirmed dead remained very low, initially just six, as officials refused to estimate how many might have died, issuing only the numbers of identified victims. In the highly charged atmosphere of anger after the blaze, there were accusations that the police and media were trying to downplay the number of deaths.

Even after the figure of 80 was issued, relatives said they were frustrated by the police’s refusal to release a full list of names of the dead and missing. In the absence of this list, survivors have been working to compile their own death toll, working with volunteer demographers and asking residents to fill in an online plan of the building. These alternative estimates range between 90 and 123, but there is no way of judging if their work is accurate.

A degree of uncertainty remains because there were people living in the block who were not registered to live there – people staying on friends’ sofas, living semi-permanently with relatives and visiting from abroad. There have also been reports of families with irregular immigration status who remain unwilling to come forward.

Police have said the landlord’s list of residents was not accurate. This week they offered an estimate of how many people should have been in the building that night, 350, of whom 255 survived and 14 were not at home.

According to the police, the names of the deceased will be published only after formal identification has taken place, with the agreement of the coroner and the family. We may have to wait until next year, when the forensic search is over, for a more accurate answer.

Since when has fire safety advice ever been to stay inside?

While the so-called “stay put” policy is counterintuitive, it has been central to fire safety advice for housing blocks since the 1950s, on the basis that such towers are made up of discrete units between which fire is not supposed to be able to spread.

A 2012 report for the Local Government Association pointed out that in 2009/10, of more than 8,000 fires in high-rise blocks, only 22 required more than five people to be evacuated.

Fire Brigades Union safety expert David Sibert has said: “The principle that tower blocks are built on is that every flat is a fire-resisting box, every flat is completely surrounded by fire-resisting construction from the rest of the building.

“So you should be able to set fire to your own flat and leave it to completely burn out and it won’t affect anybody else in the building.”

But the catastrophe at Grenfell has brought the policy under intense scrutiny. Some have pointed out that “stay put” usually features an important caveat, as in advice issued by Harlow council: “If you are in doubt – get out.” The policy has already been reviewed, after the Lakanal House fire in south London in which three women and two children died in 2009. The fire service was criticised for inconsistency in telling people to stay put or leave, but eventually the review determined that the policy should not be altered.

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After Grenfell, the picture has not been entirely consistent. The London fire brigade issued renewed guidance saying that residents are “often safer staying put”. The LGA, which represents councils, said that stay put advice was not intended to deter people from leaving if they felt threatened. And the mayor of London, Sadiq Khan, condemned the “bad advice” given to residents.

One indication of the current uncertainty can be found on the National Fire Chiefs Council website, where, if you click through from a Google search result for the stay put policy, a “page not found” message appears.

While the expert consensus is that for the vast majority of fires the stay put advice – with the caveat that those who feel threatened should leave – is correct, it is undoubtedly somewhat subjective. And it failed the residents of Grenfell catastrophically, which makes many who fear that their own towers could be at risk sceptical about the wisdom of the policy. Scrutiny of the advice will be part of the police investigation into the fire.

Why was there no helicopter with water to put out the fire from the top of the tower?

Helicopters and planes are used in some countries to dump vast quantities of water on wildfires burning over large areas where access on the ground is difficult.

But, according to Dave Sibert, the Fire Brigades Union safety adviser, “it is not an accurate way of delivering a firefighting medium”. Even if a helicopter could get close, the Grenfell Tower fire was a relatively small target in geographic terms

More importantly, no helicopter would have been able to get close to the fire, which caused flames and thick black smoke to rise into the sky. A pilot would have unable to see the tower clearly and there would have a real risk of a helicopter getting caught in the conflagration. In addition, the downdraft caused by the helicopter blades might have exacerbated the fire.

Sibert said he was “99% certain” that the London fire brigade did not have helicopters as part of its armoury. The use of helicopters to fight fires and rescue people from burning buildings was “something that happens in Hollywood, not real life”.

Why were disabled and elderly people living so high up in the tower?

Local Labour councillor Judith Blakeman said: “There were two lifts – and the Royal Borough of Kensington and Chelsea’s housing policy is that where flats are accessible by lifts, and the access is otherwise step-free, they may be deemed suitable for people with mobility problems in the absence of other accommodation.”

Some of the older tenants were longstanding residents who grew old in their flats and did not wish to move elsewhere. Many long-term residents were emotionally attached to the block, had long ties with family and friends in the area and had no desire to move.

The lifts stopped working as the fire spread, leaving a number of disabled residents unable to leave their flats. Some residents, such as Mahboubeh Jamalvatan, who has very poor mobility, had to crawl down the stairs to escape.

How many other Grenfells are there?

At least 211 residential towers over 18 metres tall in the UK are clad in similar polyethylene sandwich panels to those which burned with such ferocity on Grenfell Tower. That is how many buildings were tested by the government’s experts at the Building Research Establishment, which found all of the panels were flammable.

Among those who sent samples for testing were anxious councils and landlords who in the last decade or so joined in the trend for revamping blocks from the 1970s in an attempt to extend their lives and improve their appearance and energy efficiency. Some, such as the Chalcots estate in the London borough of Camden, which has been largely evacuated, were done under long-term PFI deals.

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We cannot yet conclude they all present the same fire risk as Grenfell Tower. After several weeks of only testing the flammability of the plastic filling of metal cladding panels, the government last week switched tack, partly under pressure from building experts who pointed out that the 100% test failure rate was not telling the industry anything new and did not take into account other potentially crucial factors

The government now wants to see if the way the combustible panels burn in combination with other elements of the cladding system affects their flammability. Six different nine-metre-tall systems built from three aluminium composite panels (with filler materials of unmodified polyethylene, fire retardant polyethylene, and non-combustible mineral) and two types of insulation (rigid polyisocyanurate foam, as was used at Grenfell, and non-combustible mineral wool) will be set alight. The idea is to replicate a severe fire in a flat breaking out of a window and examine whether it then spreads up the outside wall.

The communities secretary, Sajid Javid, has said that “for use of the panels to be safe landlords need to be confident that the whole wall system has been tested and shown to be safe”.

But cladding is not the only cause being considered. Police at Grenfell and fire safety experts at other blocks are also examining concerns over the integrity of fire doors, evacuation routes and the way gas pipes were retrofitted.

The four 24-storey blocks at Chalcots would not have been evacuated if problems with the fire doors and defects in the way gas pipes were fitted had not been spotted, according to Camden. Remedial works are under way and, while the cladding is still being removed, it was backed by non-combustible mineral wool insulation and the flammability of the whole system has not been tested. In the coming days, residents are expected to start returning, to join almost 100 families who refused to evacuate.

Who developed and promoted a building insulation foam that was not fireproof?

Celotex, a division of the French construction materials giant St Gobain, made the insulation material used on Grenfell. Chunks of the scorched and burned rigid material that sat behind the aluminium sandwich panels were found all around the area after the blaze. The company has since withdrawn it from sale for use in similar rainscreen cladding systems on buildings taller than 18 metres and halted deliveries to ongoing projects.

“Celotex is shocked by the tragic events of the Grenfell Tower fire,” the company states on its website. “Our thoughts are with everyone affected by this devastating human tragedy.”

The material is ranked class 0, in accordance with British standards, and the company’s safety information states: “The products will burn if exposed to a fire of sufficient heat and intensity. As with all organic materials, toxic gases will be released with combustion … Firefighters should attack the fire according to the combustible materials present, and use breathing apparatus.”

It was specifically tested as part of a rainscreen cladding system to British Standards BS8414-2:2005, and when installed in that way “meets the criteria set out in BRE Report BR 135 Fire performance of external thermal insulation for walls of multi-storey buildings”.

However, that system used cement panels, which are usually classed as non-combustible, rather than aluminium panels with a flammable plastic core as were used on Grenfell.

Celotex stressed that “any changes to components of the cladding system or construction methods used need to be considered by the relevant building designer”.

The works on Grenfell were designed by architects Studio E and the contractor was Rydon.

The fire in Grenfell Tower burned at 1,000C. Families are being told they may not even get the remains – not bodies – of their loved ones back to bury. Investigators cannot even find 41 of the people feared dead inside the burnt-out tower block.

The Metropolitan police took primacy in the investigation into the disaster. Grenfell’s wreckage is a crime scene, but police cannot say what crime has been committed.

Their starting point is manslaughter offences, including corporate manslaughter or gross negligence manslaughter. Offences under health and safety law may also be considered, but all these areas are complex to investigate and prosecute.

There are many questions to answer. Which of the 60 companies involved in the refurbishments over the years at Grenfell Tower did what? Who is to blame? Are they a company or individuals? And how to prove beyond reasonable doubt to a jury that a certain company or person should be convicted? Did they break a law, and are the laws even that clear cut? Or did their actions or inactions just fly in the face of common sense?

Four weeks on from the disaster, and the usual hallmarks of a criminal investigation are absent. There have been no arrests, no search warrant has been applied for, no one has been interviewed under criminal caution.

The Met say they are content with the progress, with companies and individuals voluntarily handing volumes of material over. Police vow to use harder powers if they suspect evidence is being withheld.